Currently, vehicles are provided with multiple electrical devices (loads) that are powered by a battery. These loads include loads to which a voltage that is different from an output voltage of the battery is to be applied to power the load. In order to power such a load, the vehicle is provided with a voltage converter for transforming a voltage (see, for example, JP-562-18970A).
The voltage converter disclosed in JP-562-18970A performs a step-up operation for raising an input voltage that is externally input to a voltage that is N (N.gtoreq.1) times as high as the input voltage, and a step-down operation for lowering the input voltage to a voltage that is M (0.ltoreq.M.ltoreq.1) times as high as the input voltage. The voltage that has been transformed through the step-up operation or the step-down operation is output to the load.
During the step-up operation, if an output voltage that was output to the load is lower than a reference voltage, the output voltage is raised by increasing N, and if the output voltage is higher than the reference voltage, the output voltage is lowered by decreasing N. Also, during the step-down operation, if the output voltage that was output to the load is lower than the reference voltage, the output voltage is raised by increasing M, and if the output voltage is higher than the reference voltage, the output voltage is lowered by decreasing M.
With the above-described measures, it is possible to transform the input voltage into the reference voltage, and to apply the reference voltage to the load.
As a conventional voltage converter, there is a voltage converter that performs a step-up operation and a step-down operation in parallel, and adjusts an output voltage so that an output current to be output to a load is a predetermined current.
In this voltage converter, if the output current is lower than the predetermined current, the output voltage is raised by increasing N and M, and if the output current is higher than the predetermined current, the output voltage is lowered by decreasing N and M.
In voltage converters having the above-described configuration, N and M are simultaneously increased if an output current is lower than a predetermined current, and thus an output voltage may increase excessively and the output current may largely exceed the predetermined current. Furthermore, N and M are simultaneously decreased if the output current is higher than the predetermined current, and thus the output voltage may decrease excessively and the output current may largely fall below the predetermined current.
Accordingly, the above-described conventional voltage converter has the problem that an output current repeatedly increases and decreases alternately, and is not stable.
The present invention was made in view of the above-described circumstances, and an object thereof is to provide a voltage converter that can cause an output current to stably flow.